This invention concerns a method and device for cutting a tubular part having a large diameter that is made from a rigid material, especially with an oval section, such as a cast iron, steel, plastic or fibrocement pipe.
Commonly assigned U.S. patent application Ser. No. 532,630, filed Sept. 15, 1983, describes a universal cutting method and device capable of cutting pipe of any diameter, especially cast iron pipes. Furthermore, a bevel may be cut with a preset profile. According to this method, each cutting tool is mechanically coupled with a roller so that the cutting edge of the tool and the contact point between the rotating roller and the outer wall of the tube to be cut are substantially contained in a common radial plane passing through the lengthwise axis of the tube. This arrangement displays the advantage of maintaining a constant penetration of the cutting tool into the wall of the tube even if its radius of curvature varies, for instance, if the tube is oval or elliptical. Therefore, perfectly regular bevels are obtained along the entire circumference of a part with an oval section.
The mechanical cutter for implementing this method can cut pipes over a very extensive range of diameters and therefore, in that sense, it is universal.
Such a machine is satisfactory, but in view of the number of rollers and jacks which it includes, which are scattered about the outer circumference of the tube, its cumbersomeness increases as the diameter of the tube increases. As a result, the cutter of that invention is effective but difficult to use.
The cutter of this invention is designed to achieve a simpler device and consequently it is less cumbersome and easier to use. It is especially useful for cutting pipes with large diameters, for instance which are greater than 700 mm but it is applicable for all diameters exceeding a preset minimum, for instance about 300 mm.
In the method of this invention for cutting a tubular part with a diameter exceeding a preset minimum, especially a cast iron pipe, a support frame part is equipped with rollers designed to accommodate the end of the part to be cut. Driving means rotate some of the rollers so as to make the tubular part turn about its axis while maintaining it translationally fixed. The cutting phase is executed with at least one cutting tool that is radially coupled to a roller.
According to the invention, this method is characterized in that at least one of the rollers that support the tube from below is coupled with a cutting tool. At least one pressing roller, which is introduced inside the tube, presses the tube against this supporting roller during rotation and cutting. After the cutting is completed, the inner pressing roller is withdrawn to clear the cut tube.
Thus, instead of distributing the rollers along the entire circumference of the tubular section to be cut as in the previous universal mechanical cutter, the carrier rollers are concentrated below that section, or below a horizontal plane which goes through the axis of the tubular part. The large diameter of the pipe is exploited to house inside it at least one pressing roller or "pincher", which is designed to maintain the end of the pipe against the support rollers during the cutting phase.
By concentrating the rollers below the end of the pipe, the size of the support frame for the rollers is reduced. Therefore, its cumbersomeness and its weight, as well as the number of rollers and their drive trains, are reduced. Hence, the cost of the cutting machine is also substantially reduced.
Practically speaking, the minimal diameter of the pipe which can be cut under those circumstances is about 300 mm, while its optimal diameter can exceed 1,000 mm.
However, for a specific value of the cutting angle of the tool, i.e., the angle between the tangent of the cutting edge of the tool face at the surface to be cut upon it and the perpendicular of the tangent of the surface to be cut at the contact point of the cutting edge of the tool with the surface, there corresponds a set range of acceptable pipe diameters. This set range arises from the fact that for satisfactory cutting, the cutting angle must not vary beyond the limits provided on either side of said given value of the cutting angle. Thus, cast iron of spheroidal graphite (ductile cast iron) is best cut with cutting tools of which the ideal cutting angle is about -3.degree. with a tolerance of .+-.2.degree. or 3.degree. about that value. Therefore, with an initial adjustment of the cutting angle at -3.degree., adequate cutting can be achieved for a series of pipes, the diameters of which vary, so long as the cutting angle does not exceed the above tolerance limits.
Hence, when it is desired to cut pipes for which the cutting angle might exceed those tolerances, it is necessary to proceed with a new adjustment of the cutting angle of the tool, either manually or automatically, for instance with a screw jack.
Therefore, with successive adjustments of the angular positions of the tool, a sequence of pipes can be cut for which the diameters are included more or less between the limits indicated above, the lower limit of about 300 mm being practically imposed by the requirement of introducing a pressing roller inside the pipe.